Optical amplifier and multi-core optical fiber

Abstract

The present embodiment relates to an optical amplifier and the like having a structure for enabling efficient use of pumping light while avoiding complication of a device structure. In such an optical amplifier, since pumping light from a pumping light source is supplied to each core of an amplification MCF, a coupling MCF in which adjacent cores form a coupled core is arranged between the amplification MCF and the pumping light source. The pumping light source is optically connected to a specific core of the coupling MCF, and pumping light is coupled from the specific core to remaining cores except the specific core in the coupling MCF before pumping light is supplied to each core of the amplification MCF. This enables coupling of pumping light between optically connected cores between the amplification MCF and the coupling MCF.

The invention claimed is: 
     
       1. An optical amplifier comprising:
 an amplification multi-core optical fiber having: a plurality of first cores each extending along a first central axis and comprised of silica glass doped with a rare earth element; and a first cladding surrounding each of the plurality of first cores and comprised of silica glass; 
 a coupling multi-core optical fiber having: a plurality of second cores each extending along a second central axis and optically connected to any one of the plurality of first cores, each of the plurality of second cores having a core diameter of 4 to 16 μm and an interval between adjacent ones of the second cores being equal to the core diameter or more and equal to 30 μm or less, the plurality of second cores each comprised of silica glass; and a second cladding surrounding each of the plurality of second cores and comprised of silica glass, the coupling multi-core optical fiber having a mode-coupling coefficient of 1 [l/m] or more at a predetermined pump wavelength capable of pumping the rare earth element; and 
 a pumping light source optically connected to at least one second core among the plurality of second cores and configured to supply pumping light of the predetermined pump wavelength to each of the plurality of first cores through the coupling multi-core optical fiber, wherein 
 the pumping light from the pumping light source, coupled to the at least one second core, is coupled from the at least one second core to each remaining second core except the at least one second core, and then coupled from each of the plurality of second cores to an optically connected first core among the plurality of first cores. 
 
     
     
       2. The optical amplifier according to  claim 1 , wherein
 the rare earth element includes erbium, and the predetermined pump wavelength is 980 nm. 
 
     
     
       3. The optical amplifier according to  claim 1 , wherein
 in a section of the amplification multi-core optical fiber that is taken orthogonally to the first central axis, one of the plurality of first cores is positioned on the first central axis; 
 in a section of the coupling multi-core optical fiber that is taken orthogonally to the second central axis, one of the plurality of second cores is positioned on the second central axis; 
 the pumping light source includes a single core single-mode optical fiber including a third core containing and extending along a third central axis, and a third cladding surrounding the third core; and 
 the single-core single-mode optical fiber and the coupling multi-core optical fiber are arranged such that the third core and the second core that is positioned on the second central axis are optically connected to each other, and the pump light is coupled to the remaining cores excluding the second core that is positioned on the second central axis while being propagated through the coupling multi-core optical fiber. 
 
     
     
       4. A multi-core optical fiber comprising:
 a plurality of cores each extending along a predetermined central axis and comprised of silica glass doped with a rare earth element; 
 a cladding surrounding each of the plurality of cores and comprised of silica glass; and 
 a resin coating surrounding an outer peripheral surface of the cladding, wherein 
 each of the plurality of cores has a core diameter of 4 to 16 μm, 
 an interval between adjacent cores of the plurality of cores is equal to the core diameter or more and equal to 30 μm or less, and 
 the multi-core optical fiber has a mode-coupling coefficient of 1 [l/m] or more at a wavelength of 1550 nm as an index indicating a coupling state between the adjacent cores among the plurality of cores. 
 
     
     
       5. The multi-core optical fiber according to  claim 4 , wherein the plurality of cores include one core extending along the predetermined central axis in a state including the predetermined central axis.